Finding sum in Crystal Report based upon some condition

Thanks a lot for your time and consideration.  I could display those totals based upon the value of A2 using running total.
A2 actually holds two values 0 and 1. What i needed was a seperate total depending on its value. Thanks for your help.
 But now I've another problem depending on the same. If the total i got is greater than 12 i need to display only 12 and if its less than 12 i need to display the actual value.
Where and how should i give that condition as i have displayed the total using running total??

THANKS.. I've done it. Can u please let me know how to check whether a field value is NULL or not.. I mean, say, i need to check if A2 is null or not. And if its NULL i need to consider it as 0. I used NVL functions but didnt get it working.

create a formula field... A2_Calc
if {A2} = 1 then {A2} else 0

Another formula field A2_Calc_Total
create a summary field in the report group and point it to A2_Calc - Want to Hide this field so it doesnt actually print.
Then create a new formula - then show the report fields and double click the new formula summary of A2_Calc, then change it into the appropriate if

if( Sum ({@A2_Calc}, {@Group}) ) > 12 then Sum ({@A2_Calc}, {@Group}) else 0  

select ({A.a2})
case 1 :
"TYPE1"
default:
"TYPE2"

Actually what i want is to display a column depending on A2's value. But it displays correctly for all rows which has 0 or 1 value. It isnt considering the null valued rows. I need to display as "TYPE2" if its 0 or null. Can you correct me the above code.

thank you peter i have done it..
Again, when i take the total of a column using the running total i have added a condition (use a formula in running total)  like A2=1.. But if the column doesnt contain any row with A2=1 its displaying the result empty. Instead of displaying it empy i need the total to be displayed as 0.0..

So please lemme know what should i do for displaying likewise...

Sorry, that should be

if (isnull({A2}) or {A2} = 0) then "TYPE 2" else "TYPE 1"

Mark, i got it displayed as type1 or type2.. Now my problem isnt that.
I have a running total field F1 and i have taken the sum of a field say a1 depending on the value of a2. I mean, i have given in the formula field of the running total as A.a2=1 (where A is the table name) .
What i want is I need the the total to be displayed as 0.00 if there is any row satisfying the condition A2=1.
For a particular record there is no such row with a2=1..Hence what is it displaying now is just a blank box in the final report. I need to display 0.0 instead of that. Can you please get me a solution for that??
Hope you got what i meant.

THANKS A LOT FOR YOUR GREAT HELP. Everything is working fine for me.